Silver recovery system

ABSTRACT

Silver is recovered from spent photographic solutions by feeding the spent solutions into a pre-collecting vessel where the solution collects until a predetermined volume has been received, at which time it is automatically dispensed, by a self-triggering syphon, into an electroylsis chamber, and direct current is automatically turned on for a predetermined period of time between an anode and a cathode in the chamber to plate out the silver onto the cathode. A magnetic agitator is automatically energized to keep the silver suspended.

United States Patent 11 1 1111 Burgess Dec. 16, 1975 [54] SILVERRECOVERY SYSTEM 3,715,291 2/1973 Bentley 204/275 X [75] Inventor:Kenneth G. Burgess, Derby, N.Y.

Primary Examiner-John H. Mack [73] Ass1gnee: Hydrospace Industr1es,lnc.,Buffalo, Assistant w 1 Solomon Attorney, Agent; or FirmRaymond F. Kramer[22] Filed: Apr. 12, 1973 21 Appl. No.2 350,464 [571 ABSTRACT Silver isrecovered from spent photographic solutions [52] U5. CL 204/229,204/109, 204/273, by feeding the spent solutions into a pre-collecting204/275, 204/294 vessel where the solution collects until a predeter- 51Int. cm czsc 7/00 mined mlume has been received which time is 58 Fieldof Search 204/109 229 261 273 automatically dispensed by aself'triggering P 2 I275 into an electroylsis chamber, and directcurrent 1s automatically turned on for a predetermined period of [56]References Cited time between an anode and a cathode in the chamber toplate out the silver onto the cathode. A magnetic 2 563 903 S Z STATESPATENTS agitator is automatically energized to keep the silver l l Zadra204/275 X sus ended 3,477,926 ll/l969 Snow et al. 204/109 p 3,694,3419/1972 Luck, Jr 204/273 18 Claims, 7 Drawing Figures US. Patent Dec. 16,1975 Sheet2of3 3,926,768

FIG. 5

FIG. 6

llf/f/l/ US. Patent Dec. 16, 1975 Sheet 3 of3 3,926,768

INPUT BINARY T l I I I I I U P DOW N COUNTER us TIMER "0 V. AC.

FIG. 7

SILVER RECOVERY SYSTEM BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to silver recovery from spentphotographic solutions, and in particular to an automatic,operator-less, system particularly useful for recovering silver fromspent X-ray developing solutions ules. The intensity of the light willdetermine the number of metallic silver atoms formed. Granules of thesilver bromide containing metallic silver are sensitized, and can bereduced to metallic silver by an organic agent known as developer. Thedeveloper reduces the exposed granules more easily than the unexposedgranules, and by chemically controlling the developer action, thenon-sensitized regions of the film remain unchanged. The film now passesthrough a second chemical, known as fixer, where a second and veryunique action occurs. The unsensitized areas are, of course, still madeup of silver bromide and/or chloride, which is able to react with thechemical fixer, causing a washing of the silver from these unsensitizedareas of the film. The number of silver granules washed away isdependent upon the density of the unsensitized granules in any' oneregion of the film. In photographic studios, motion picture labs,industrial X-ray centers and hospitals, this silver is passed out of theprocessor into a number of differing types of silver recovery systems,or directly into the drain.

To date, the most popular system of silver recovery in institutions suchas hospitals has been the canister method. The system is veryineffective for a number of reasons. The canister is nothing more than abucket, ranging in capacity from 5 to 50 gallons, containing iron woolwith a number of passages through it, depending upon the manufacturersdesign. As the silverladen solution passes through the iron wool, theiron ions replace the silver ions in solution, and metallic silver inthe form of sludge appears within the iron mesh. The silver is combinedwith'a number of other chemicals and chemical compounds, iron and ironsulfide, as an example, and a multi-stage refining operation is requiredbefore any acceptable level of silver purity is attained. The cost ofthe system is relatively small, varying, depending on size, between$16.00 and $200.00, but it can never be re-used. Additionally, thecanister method has a limited life, because only a certain number ofgallons of solution can pass through it before all of the removalproperty is gone. The canister also decreases in efficiency with age,due to internal oxidation and a number of physical reactions undergoneas the solution deposits silver in the iron mesh. Typical efficiencyaverages about 30-70% of the total recoverable silver passed into thecanister in solution. Typical life expectancy for such a unit in ahospital would be 1 month.

A second system for removing silver from solution is called zincing. Thesystem consists of salting or doping large quantities of spent hyposolution with zinc flakes. The solution is then drained off, leavinglarge quantities of precipitated silver sludge, which must, in turn, berefined. The operation of this system requires that the participatinginstitutions store solutions and sell them to a zincing operation at afraction of the solutions silver worth. In addition, the system islaborious and space-consuming, requiring large users of hypo solution tomaintain considerable storage facilities in usually critically neededspace. The system is a source of marginal revenue in most cases,considering the worth of the silver contained in such solutions.

The third system available to remove silver from hypo solutionsiselectrolysis, or electroplating. This system has the capability ofbeing the most efficient of all processes, due to the fact that thesilver is reclaimed in nearly pure form (92-98%). The basic system hasseveral disadvantages. It involves largecapitol outlay. and only whencomparatively maintenance-free can the unit demonstrate superiority. Theprior art machinery normally marketed does not contain an automatedcontrol apparatus due to cost, and requires considerable attention. Ifthe'machine is left unattended, it will continue at a given currentlevel regardless of fluidflow or solution density, and will decrease inefficiency by losing silver, or begin to cause sulfidization, gasemission and destruction of the purity of the silver already plated.Operation at current levels too high for need place undue strain on allparts of the machinery and resulting gases emitted can causeconsiderable discomfort in the area in which the machinery is located.Such phenomenon, production of hydrogen sulfide, causes a noxious rottenegg smell.

Machines have been marketed with a number of control mechanisms,including impedance control. All require secondary adjustment and areconsiderably more expensive due to this additional equipment. Prior artmachinery employs, for agitation, rotation of the cathode or rotation ofthe anode. Such systems require motorization large enough to carry thefinal full laden weight of the respective element and in additionrequire direct mechanical connections to be made in a difficultatmosphere. The cathode rotation system also requires that rotation bemaintained at a significant speed, most commonly rpm, which may, due tocentrifugal forces involved, cause premature flaking from the cathodeand may retard plating efficiency in low silver density concentrations.

It is a primary object of the present invention to provide an improvedsilver recovery unit that is not subject to the above-mentioneddisadvantages of the prior art and that, in particular, has stationaryand easily removable cathode and anode.

It is another object of the present invention to provide an improvedsilver recovery system which operates automatically, without thenecessity for an operator, which does not produce any noxious gasestherefrom and which is easily serviced for checking and removing theamount of silver plated out.

SUMMARY OF THE INVENTION A method and apparatus for recovering silverfrom spent photographic solutions (particularly spent photographicsolutions from X-ray development in hospitals) is provided wherein thespent solutions are fed, as they are generated, into a pre-collectingvessel of the silver recovery unit. The pre-collecting vessel holds thespent photographic solution until a predetermined volume is collected,at which time it is automatically dispensed into an electrolysis chamberand a current is automatically passed between a cathode and an anode inthe electrolysis chamber for a predetermined period of time to plate outthe silver on the cathode. The silver is kept suspended (during the timethat the current is on) by a magnetic agitator located in the bottom ofthe electrolysis chamber. A discharge opening is located at the top ofthe electrolysis chamber to maintain the chamber full, up to apredetermined level. The cathode may be graphite of a parabolic shape invertical section to provide good silver suspension and to minimizefrothing. A hinged cover is located over the electrolysis chamber foreasy viewing of the chamber. The cathode and the anode are both easilyremoved by simply pulling them upwardly out of the chamber. Thepre-collecting vessel includes a floating magnet and a pair ofvertically spaced-apart magnetic reed switches properly located inrelation to a self-triggering syphon that automatically dispenses apredetermined volume of the solution into the electrolysis chamber.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be morefully understood by reference to the following detailed descriptionthereof, when read in conjunction with the attached drawings, whereinlike reference numerals refer to like elements, and wherein:

FIG. 1 is a cutaway partly cross-sectional elevation view of theapparatus of the present invention;

FIG. 2 is a cross-sectional elevational view of the apparatus shown inFIG. 1 along lines 22 of FIG. 1;

FIG. 3 is a plan view looking down into the apparatus of FIGS. 1 and 2;

, FIG. 4 is a cross-sectional view of the pre-collecting vessel of thepresent invention;

FIG. 5 is a horizontal cross-sectional view of the pre-collectingvessel;

FIG. 6 is a plan view of the magnets used in the magnetic agitator; and

FIG. 7 is a schematic block diagram of an electric circuit used in thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now tothe drawing, a brief overall description of the apparatus will first beprovided. followed by a detailed description of each element thereof.FIGS. l-3 show a silver recovery unit l0made according to the presentinvention and including a base 12 and a cover 14 hinged at 16 to thebase. Spent photographic solution is fed into the unit through an inlettube 18 in the top of the cover 14 by means of a coupling (not shown) onthe end of the tube 18. The tube 18 feeds the solution into apre-collecting vessel 20 where it remains until a predetermined volume(such as 800 ml) has built up, at which time the solution isautomatically dispensed into an electrolysis vessel 22 having a chamber24. After the solution is dumped into the chamber 24, current isautomatically turned on, for a predetermined time period. between ananode 26 and a cathode 28 to plate out the silver on the cathode 28. Thechamber 24 is kept full up to a level determined by a discharge tube 30.During the time the current is on, a magnetic impeller 32 in the bottomof the vessel 22 is energized to keep the solu- 4 tion agitated to keepsilver from falling by gravity in the bottom of the chamber 24.

Referring now in detail to the various elements of the unit 10, the base12 includes a housing 34 having a support 36 for supporting theelectrolysis vessel 22 therein. The housing 34, electrolysis vessel 22,and the cover 14 are preferably made of fiberglass, such as 197A, Hetronfiberglass, which is impervious to mild acids and gases. The unit 10 hasa wrinkle finish rendered in black to be non-reflective for specific usein the darkroom. The electrolysis vessel 22 has no opening in its lowerend, the only discharge opening being discharge tube 30. Theelectrolysis-vessel 22 does have a central, vertical, support tube 38which supports the cathode 28. The bottom wall 40 of the electrolysisvessel 22 includes a recess '42 with a pair of bearing rings 44,preferably of Teflon, in the bottom thereof.

The impeller 32 is rotatably mounted about the support tube 38 in therecess 42. The cathode 28 has a central axial opening 46 therein havinga depth such that a bottom end 48 of the cathode 28 is spaced above(approximately three-fourths inch) the impeller 32.

The cathode 28 is preferably of HC type solid graphite, about 6 inchesin diameter at the top, and has a parabolic shape (hereby defined toinclude a truncated parabolic shape and similar curved shapes) invertical section, as shown in FIG. 2, with the apex adjacent the bottomof the electrolysis chamber 24. The cathode 28 has a handle 50,preferably ofstainless steel, to aid in pulling the cathode up out ofthe chamber 24, as when it is time to remove the silver that has platedout on the cathode. The electrical connection 52 is attached to one ofthe screws used to connect the handle 50 to the cathode. The parabolicshape of the cathode provides a good homogeneous mixture with goodsuspension of the silver while minimizing frothing. The cathode 28 is aparabolic shaped configuration made of HC type graphite for goodconductivity, low cost, durability, and unexpected minimization ofsulfiding. In one example. after most of the silver had been plated thesame high current was left on, producing, with other than the graphitecathode of the present invention, much hydrogen sulfide gas, andunexpectedly, very little hydrogen sulfide gas was produced when thecathode was a graphite cathode. The parabolic bottomis constructed toinduce constant flow patterns without unnecessary turbulence. It isimportant that the solution be continually mixed as silver ions near thecathodes are removed toinsure a homogenous mixture without foaming. Thecathode material has been determined to be instrumental in platingefficiency, especially in a start-up situation. For this purpose agraphite cathode was found to be the most acceptable. With this materialthe formation of hydrogen sulfide gas (H S) is greatly reduced andsulfiding is reduced by an extreme factor. It was found that a graphiteelectrode allowed overage in current by from calculation with verylittle sulfiding and production of H S gas.

The anode 26 is preferably a flat stainless steel sheet folded into acylindrical shape and inserted into the chamber 24 and allowed to,unwind up against the sidewall of the chamber 24. An electricalconnector 54 is provided at the top of the anode 26. A slot 56 isprovided in the anode 26 in alignment with the discharge tube 30. Theanode 26 can be removed from the chamber 24 by simply lifting up thecover 14, disconnecting an electrical lead 58, and pulling the anodedirectly up out of the chamber 24. To aid in removal,

the anode 26 can be formed into a smaller cylinder before removal.Stainless 316 anodes are a special addition to the plating fieldthemselves, becasue of their extremely long life expectancy in hyposolutions. There is an initial inherent problem in plating withstainless, and for this reason the anode 26 is preplated with silver.Without preplating, primary plating on a clean cathode would requirehigh density silver laden solution to achieve desired platingefficiency.

To keep the silver in suspension, the unit has an agitator 60 includinga motor 62 mounted under the bottom wall 40 of the electrolysis vessel22. The motor is connected to a cooling fan 63 and to an inducing magnet64 located just below the impeller 32. The impeller 32 includes a magnet66 and vanes 68, preferably made of Plexiglas, and connected to the topof the magnet 66 as by epoxy glue. The inducing magnet 64 and theimpeller magnet 66 each are made as shown in FIG. 6. FIG. 6 shows aceramic ring (for example of barium carbonate and iron oxide) that ismagnetized on one surface only thereof in the manner shown in FIG. 6. Inthe inducing magnet 64 the top surface is magnetized and in the impellermagnet the lower surface is magnetized. By this magnet, greaterefficiency is achieved by utilization of a circular field concentric tothe rotational movement of the magnet. The magnet 64 maintains aconstant distance-torque parameter. The distance between the adjacentsegments is a constant, while in prior art magnetic agitation magnetsusing bar magnets, the distance between adjacent ends is greater at theoutside than at the inside, i.e., the gap tapers outwardly in widthrather than being of constant width.

The agitation system of the present invention gives maximum agitationwithout breaking the surface of the liquid and causing foaming. Theagitator is also designed to induce maximum mixing with the least amountof rotation. This system is significantly superior to the standardrotating cylindrical cathode design which, due to its dynamicproperties, causes cylindrical rotation with little true mixing of thesolution. To achieve maximum mixing, the interior mixing magnet 66 hasvanes 68 of unequal height, but with equal area, causing strongturbulence radiation from the impeller The pre-collecting vessel ispreferably made of plexiglass and is mounted under the cover 14. Thepre-collecting vessel 20 includes a self-triggering syphon 70 forautomatically dispensing solution from the pre-collecting vessel to theelectrolysis chamber 24 after a predetermined volume of solution hascollected in the pre-collecting vessel. The pre-collecting vessel 20also includes a reed switch package 72 for sensing when the solution isfed to the electrolysis chamber 24 and for feeding the released volumeinformation to an up-down counter l 14 (see FIG. 7) that switches on thecurrent to the electrodes 26 and 28 for a predetermined period of time,and for energizing the agitator 60.

Referring now to FIGS. 4 and 5, the syphon 70 includes an inverted tube74 having an opening 76 spaced from a bottom wall 78 of thepre-collecting vessel 20 and supported by an arm 80. Positioned insideof the tube 74 is a smaller tube 82 extending down through the bottomwall 78 in fluid tight relationship therewith. The top of the smallertube 82 is connected to the larger tube 74; however, the smaller tube 82has a serrated (or scalloped) edge 84 to allow fluid to pass from insideof the tube 74 to inside of the tube 82. The

6 syphon also includes a tube 85 slidably fitted inside of tube 82. Thetube 85 can be slid up beyond the bottom of the serrated edge 84 to varythe size of the openings through the serrations to set the syphon startpoint for variations in surface tension.

In operation, solution feeds into the pre-collecting vessel 20 throughthe inlet tube 18, and collects in the vessel 20 until the level risesabove the serrated edge 84 at which time a syphon action takes place andthe solution feeds out of the vessel 20 through the tube 82, until thelevel in the vessel 20 reaches the level of the opening 76. Thepre-collecting vessel thus automatically collects solution andautomatically dispenses a predetermined volume thereof (for example, 800ml.) into the electrolysis chamber 24. Any volume can be dispensed, aslong as the circuitry is designed (or adjusted) with this amount ofsolution and consequently with this amount of silver, in mind.

The inlet tube 18 of the cover mounted pre-collecting vessel 20 ispositioned to allow the cover to be hinged open with no spillage or lossof solution.

The reed switch package 72 comprises a tube 86 (sealed from any liquidin the vessel 22) in which are positioned upper and lower magnetic reedswitches 88 and 90. A float 92 with a central axial bore is locatedabout the tube 86 and includes a pair of magnets 94, for actuating theswitches 88 and 90. The reed switching unit 72 is a dual unit, havingone activator at the bottom of the float stroke and one 88 at the top toensure that liquid bounce will not activate it. After the top positionis met, the syphon 70 reaches its critical measuring point and dispensessolution. However, the switches 88 and 90 do not initiate the currentuntil the fluid level drops and the lower switch 90 is activated insequence after the upper switch 88 has been activated.

The unit 10 also includes a fliter and a full wave rectifier 96 belowthe electrolysis vessel 20. A front compartment 98 is connected to thehousing 34 by hinges 100 and includes an ammeter 102, an on-off switch104, and a red light 106 to indicate when the unit is on. Wiring to theelectrodes 26 and 28 extends through this compartment 98.

FIG. 7 shows, schematically, an electrical circuit used in the presentinvention; it will be readily understood by one skilled in the art. Thecircuit includes the reed switch package 72, including the float 92 andthe reed switches 88 and 90, the agitator motor 62, and the cathode 28and anode 26. The pre-collecting vessel 20 receives hypo and stores ituntil the self-triggering syphon 70 is tripped. Just before the syphon70 is tripped, the magnetic float 92 which follows the level of thehypo, causes the upper switch 88 to close and this pulse satifiesone-half of the required function to turn the system on. After theliquid is dumped and the level reaches its lowest point, the float 92causes the lower switch 90 to close completing the requirements to storeone bit of information (the switches must close in that order). Thestorage of a bit sets the unit in operation. by an electronic switch 112controlled by an up-down counter l 14, and continues the electrolysisfor a preset time by means of a timer 116, for each bit received.

The unit 10 is designed for the reclamation of silver from photographic(hypo) solutions, removes from to 99% of all contained silver, and doesso at purity levels of 92% or better in both high and low densitysolutions.

The unit is self contained, powered by either 1 lOVAC or 22OVAC, or withthe addition of a portable power pack, nearly any DC voltage above 6v.The unit in full operation uses approximately 75 to 80 watts. Undernormal conditions, the unit will use an average f watts, orapproximately 0.72 Kw-hrsper 24 hour period. The wattage drawn dependsupon pre-set current densities in the machine itself. Due to a number ofunique features, this machine can efficiently cope with a wide varietyof work loads. including sporadic major and minor loads. The machine isan on-site system, connected directly to X-ray or photographicprocessing equipment.

As'will be seen from the above description, the present inventionprovides a silver recovery unit that: (l) employs completely enclosedelectrical and mechanical components, (2) employs a fiberglass casingthat is impervious to mild acids and gases and which maintains a goodappearance and durability, (3) includes individually removable anode andcathode for maintenance, cleaning and silver removal, (4) employsmagnetic agitation to insure maximum isolation of motors and mechanicaldrive systems from corrosive gases and liquids and to insure non-leakagein the drive system, (5 employs a parabolic tipped cathode to insuremaximum good'mixing while reducing foaming, (6) employs a stainlesssteel anode which can be plated with silver when necessary for maximumplating efficiency during start-up even in light density solutions, (7)employs a pre-collecting vessel with a self-triggering syphon start anda break point system coupled electromechanically for automaticallydispensing a predetermined volume of solution into the electrolysischamber, and for turning on the current to the electrodes at apredetermined time period respectively, (8) provides a hinged cover toallow quick and easy check of the silver collection without having toremove either the cathode or the anode, and (9) employs a graphitecathode having the properties described above.

The invention has been described in detail with particular reference tothe preferred embodiment thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described hereinabove and as defined in the appendedclaims. For example, other types of precollecting vessels can be usedother dispensers than the syphon 70 can be used and other switch meanscan be used in place of thefloat and magnetic reed switch 72. Othertypes of agitation can be used to maintain the silver suspended. Forpurposes of the present specification and claims, the term loosely asapplied to the electrodes 26 and 28, is defined to mean unconnectedbyany structural element, that is, the loose electrodes 26 and 28 can belifted directly out of the vessel 22 without first having to disconnectthem from any structure (the electrical leads are not a structuralelement").

I claim:

1. An apparatus for recovering silver from spent photographic solutionscomprising:

a. an electrolysis vessel having an electrolysis chamber therein;

b. an electrode removably positioned in said vessel adjacent a wallthereof;

c. an electrode of opposite sign positioned at or near the center ofsaid vessel; I

d. an impeller located within said vessel adjacent to or near the bottomthereof;

6. means for rotating said impeller:

f. a pre-collecting vessel positioned above the electrolysis chamber andincluding means for receiving spent photographic solution to be fed intosaid chamber and siphon means for dispensing a predetermined volume ofsaid solution into said chamber; and 1 g. means for-passing an electriccurrent between said electrodes and through the solution in saidelectrolysis chamber for a predetermined period of time in response tothe dispensing of said volume of solution from the pre-collecting vesselinto the chamber.

2. An apparatus according to claim 1 wherein the centrally positionedelectrode is graphite.

3. An apparatus according to claim 1 wherein the centrally positionedelectrode is of a parabolic shape in vertical cross-section with itsapex adjacent the impeller. I

4. An apparatus according to claim 1 wherein the rotating meanscomprises means for magnetically rotating the impeller.

5. An apparatus according to claim 1 wherein the electrolysis vesselincludes an exit opening in a side wall thereof adjacent the topthereof.

6. An aparatus according to claim 1 wherein the impeller includes aplurality of vertical vanes of equal centrally positioned electrode hasan opening in its lower end.

10. An apparatus according to claim 9 wherein the centrally positionedelectrode has a parabolic shape in vertical cross-section with its apexadjacent the impeller.

11. An apparatus according to claim 10 wherein the impeller is circularand the rotating means comprises means for magnetically rotating theimpeller.

12. An apparatus according to claim 11 wherein the centrally positionedelectrode is the cathode.

13. An apparatus according to claim 1 wherein the pre-collecting vesselincludes a self-triggering siphon for dispensing photographic solutioninto said electrolysis chamber after a predetermined volume of solutioncollects in said-collecting vessel.

14. An apparatus according to claim 13 wherein the means for passing anelectric current between the electrodes and through the solution in theelectrolysis chamber for a predetermined period of time in response tothe dispensing of a volume of solution from the pre-collecting vesselinto said chamber includes switch means in said pre-collecting vessel.

15. An apparatus according to claim 14 wherein said switch meansincludes a pair of vertically spaced-apart magnetic reed switches.

16. An apparatus according to claim 15 wherein the electrode removablypositioned in the electrolysis vessel and adjacent a wall thereof isessentially cylindrical and is positioned adjacent the inner side wallof the 10 them so that photographic solution can rise in the annulusbetween the tubes as it rises in the pre-collecting vessel, saidcylinders being closed across the tops thereof and having a passagewaybetween them at the tops thereof to permit siphoning flow of solutionfrom the pre-collecting vessel body of solution, through the annulus,the passageway and the internal tube to the electrolysis chamber.

1. AN APPARATUS FOR RECOVERING SILVER FROM SPENT PHOTOGRAPHIC SOLUTIONSCOMPRISING: A. AN ELECTROLYSIS VESSEL HAVING AN ELECTROLYSIS CHAMBERTHEREIN; B. AN ELECTRODE REMOVABLY POSITIONED IN SAID VESSEL ADJACENT AWALL THEREOF; C. AN ELECTRODE OF OPPOSITE SIGN POSITIONED AT OR NEAR THECENTER OF SAID VESSEL; D. AN IMPELLER LOCATED WITHIN SAID VESSELADJACENT TO OR NEAR THE BOTTOM THEREOF; E. MEANS FOR ROTATING SAIDIMPELLER; F. A PRE-COLLECTING VESSEL POSITIONED ABOVE THE ELECTROLYSISCHAMBER AND INCLUDING MEANS FOR RECEIVING SPENT PHOTOGRAPHIC SOLUTION TOBE FED INTO SAID CHAMBER AND SIPHON MEANS FOR DISPENSING A PREDETERMINEDVOLUME OF SAID SOLUTION INTO SAID CHAMBER; AND G. MEANS FOR PASSING ANELECTRIC CURRENT BETWEEN SAID ELECTRODES AND THROUGH THE SOLUTION INSAID ELECTROLYSIS CHAMBER FOR A PREDETERMINED PERIOD OF TIME IN RESPONSETO THE DISPENSING OF SAID VOLUME OF SOLUTION FROM THE PRE-COLLECTINGVESSEL INTO THE CHAMBER.
 2. An apparatus according to claim 1 whereinthe centrally positioned electrode is graphite.
 3. An apparatusaccording to claim 1 wherein the centrally positioned electrode is of aparabolic shape in vertical cross-section with its apex adjacent theimpeller.
 4. An apparatus according to claim 1 wherein the rotatingmeans comprises means for magnetically rotating the impeller.
 5. Anapparatus according to claim 1 wherein the electrolysis vessel includesan exit opening in a side wall thereof adjacent the top thereof.
 6. Anaparatus according to claim 1 wherein the impeller includes a pluralityof vertical vanes of equal areas and different shapes.
 7. An apparatusaccording to claim 1 wherein the removably positioned electrode is aflat stainless steel sheet bent into cylindrical form and inserted intosaid chamber, which is readily removable therefrom.
 8. An aparatusaccording to claim 7 wherein the removably positioned electrode includesan electrical connection at a top portion thereof and includes anopening in a side wall thereof mating with an exit opening in theelectrolysis vessel.
 9. An apparatus according to claim 1 wherein thecentrally positioned electrode has an opening in its lower end.
 10. Anapparatus according to claim 9 wherein the centrally positionedelectrode has a parabolic shape in vertical cross-section with its apexadjacent the impeller.
 11. An apparatus according to claim 10 whereinthe impeller is circular and the rotating means comprises means formagnetically rotating the impeller.
 12. An apparatus according to claim11 wherein the centrally positioned electrode is the cathode.
 13. Anapparatus according to claim 1 wherein the pre-collecting vesselincludes a self-triggering siphon for dispensing photographic solutioninto said electrolysis chamber after a predeteRmined volume of solutioncollects in said-collecting vessel.
 14. An apparatus according to claim13 wherein the means for passing an electric current between theelectrodes and through the solution in the electrolysis chamber for apredetermined period of time in response to the dispensing of a volumeof solution from the pre-collecting vessel into said chamber includesswitch means in said pre-collecting vessel.
 15. An apparatus accordingto claim 14 wherein said switch means includes a pair of verticallyspaced-apart magnetic reed switches.
 16. An apparatus according to claim15 wherein the electrode removably positioned in the electrolysis vesseland adjacent a wall thereof is essentially cylindrical and is positionedadjacent the inner side wall of the electrolysis chamber so that it canbe removed directly upwardly from said chamber.
 17. An apparatusaccording to claim 16 wherein the electrode is a flat stainless steelsheet bent into a cylinder and inserted in said chamber and can beremoved by bending it into a smaller cylinder and pulling it directlyupwardly out of said chamber.
 18. An apparatus according to claim 13wherein the self-triggering siphon includes external and internalvertical tubes with an annular passageway between them so thatphotographic solution can rise in the annulus between the tubes as itrises in the pre-collecting vessel, said cylinders being closed acrossthe tops thereof and having a passageway between them at the topsthereof to permit siphoning flow of solution from the pre-collectingvessel body of solution, through the annulus, the passageway and theinternal tube to the electrolysis chamber.